Compositions and Methods for Treating Cellulose Based Materials with Micronized Additives

ABSTRACT

A composition for treating cellulosic materials is provided. The composition comprises a dispersion of micronized additives. The dispersion comprises additive particles with diameters in the range of 0.001 to 25 microns. Also provided is a method for the application of the additive-containing composition to wood, as well as wood products which have been treated with the composition.

CROSS REFERENCE TO RELATED APPLICATION

Applicant hereby claims priority to U.S. Provisional Application No.60/570,659, filed on May 13, 2004, which is incorporated herein byreference.

BACKGROUND

Wood and wood-based substrates, such as paper, particleboard, woodcomposites, plastic lumbers, rope, etc., are often treated in order toimpart desired characteristics to or enhance existing characteristics ofthe substrate. Non-limiting examples of performance characteristicswhich can be imparted or enhanced by treatment of a substrate withadditives are durability, fire resistance and water resistance.Non-limiting examples of such appearance characteristics are color andtexture. Non-limiting examples of additives which can be applied arecolorants, pigments, polymers, water repellants, dimensional stabilizingagents, UV inhibitors, UV absorbers, UV blockers, antioxidants, fireretardants and biocides, such as, for example, insecticides, fungicides,moldicides, algaecides and bactericides.

Many, if not most such additives have little or no water solubility andare thus difficult to apply to wood as a water-based solution.Generally, such additives have been dissolved in organic carriers priorto use, often with the additional step of emulsification in water by theuse of various surfactants if a water-based application is desired.

Solubilizing agents or surfactants such as emulsifying agents, wettingagents, etc. are added in order to give a product that can be applied asa water-based composition to wood or cellulosic substrates. However,solubilizing agents or surfactants, etc. are costly and the use of theseproducts may also result in enhanced leaching of additive upon exposureof treated wood to moisture. It is thought that the enhanced leaching isdue to the fact that solubilizing agents, surfactants, emulsifyingagents, wetting agents, etc. remain in the wood after treatment. Uponexposure to moisture, the additives are solubilized or otherwisemobilized, and leach from the wood.

Despite the efforts of many inventors, there remains a need for organicpreservative systems which do not require organic solubilizing agents,which are suitable for use in the treatment wood and cellulose-basedmaterials, and have only low levels of leaching, if any, upon exposureof treated materials to the environment. This need is satisfied by thecompositions disclosed herein

SUMMARY OF THE INVENTION

Disclosed herein are compositions which comprise micronized additives.Also disclosed is a method for the use of the compositions to treatcellulosic materials, particularly wood.

Current technology typically requires the addition of organic solvents,emulsifying agents, etc. Disadvantages of the typical approach used inthe art include increased cost, residue bleeding, environmental damageand harmful exposure to leached additive.

With the inventive compositions disclosed herein, organic solvents andemulsifiers are not required, thus reducing cost. Furthermore, leachingof additives from treated materials is reduced relative tonon-micronized or solubilized compositions currently used in the art,thus reducing environmental and exposure risks.

Also provided is a method for the treatment of wood or wood product withthe compositions of the present invention. In one embodiment, the methodcomprises the steps of 1) providing a mixture comprising micronizedadditive particles in an aqueous carrier, such as in the form of adispersion, emulsion, suspension, or other particle/carrier combination,and 2) applying the particles to a wood or wood product. In a furtherembodiment, the particulate additives have been prepared by the grindingof the additive, optionally in non-micronized particulate form, inwetting agents and/or dispersants such that the additive is reduced tothe form of micronized particles. When such a composition is used forpreservation of wood, there is minimal leaching of the additive fromwood as described herein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts the anatomy of coniferous wood. A: Resin canal; B:Earlywood tracheids; C: Latewood tracheids; D: Bordered pits.

FIG. 2 depicts the border pit structure for coniferous woods.

RIGHT: Microscopic view of the cross section of a bordered pit.

LEFT: Torus in top view. The torus is supported by a net of radialfibril membrane, also called the margo. The flow of fluids between twotracheids through such a membrane is restricted by the size of themembrane openings. A: Pit aperture; B: Torus; C: Margo (microfibrils);D: Pit border

DETAILED DESCRIPTION OF THE INVENTION

Unless stated otherwise, such as in the examples, all amounts andnumbers used in this specification are intended to be interpreted asmodified by the term “about.” Likewise, elements or compounds identifiedin this specification, unless stated otherwise, are intended to benon-limiting and representative of other elements or compounds generallyconsidered by those skilled in the art as being within the same familyof elements or compounds. Also, the term “additive” refers to waterrepellants, coloring agents, UV stabilizers, UV absorbers, UV blockers,antioxidants, dimensional stabilizing agents, fire retardants or otherorganic or inorganic compounds which enhance appearance or performancecharacteristics of the wood.

Disclosed herein is a micronized additive composition and method for usethereof in treatment of cellulosic material, and in a preferredembodiment, wood. Unlike wood which has been treated with additivessolubilized in organic solvents or other solubilizing agents, woodtreated with compositions of the present invention have little or noemission of organic solvent. Furthermore, upon exposure to moisture, theleaching of the additive from treated wood is generally significantlyless than that associated with solubilized compositions.

Non-limiting examples of additives which can be used are inorganic ororganic additives, such as organic pigments, inorganic pigments, waxes,polymers, anti-weathering agents (such as, for example, UV absorbers, UVblockers, UV inhibitors, antioxidants), fire retardants and mixturesthereof. Non-limiting examples of additive chemical types to which thisstrategy has been applied are azoles, carbamates, isothiazolinones,thiocyanates, sulfenamides, quaternary phosphonium compounds, quaternaryammonium compounds, nitriles, pyridines, etc. and mixtures thereof.

Inorganic or organic pigments, water repellants, anti-weathering agents,dimensional stabilization agents, and fire retardants, etc. and mixturesor synergistic mixtures thereof having relatively low solubility can beused with the system and are well known to those skilled in the art andinclude those listed in the tables below. In general, it is preferablefor the additive to comprise particles of sizes in the range of 0.001microns to 25 microns and a relatively low solubility in water. A watersolubility which is less than 0.5 g of biocide per 100 grams of water at25° C. is preferred. Such additives are referred to hereafter as“suitably insoluble.”

In general, an “additive” is defined to be a component which is appliedto wood as part of a solution. In an embodiment of the presentinvention, the additive is in addition to a component which has biocidalactivity. An additive can, itself, have biocidal ability, and be aco-biocide. An additive may instead be a non-biocidal compound includedto enhance the performance or appearance characteristics of the wood towhich it is to be applied. An additive may also be a component whichdoes both, i.e., has biocidal activity and also improves an appearancecharacteristic of the wood. Those of skill in the art will recognizethat many compounds have both characteristics.

Non-limiting examples of suitably insoluble inorganic pigments include:iron oxides, including red iron oxides, yellow iron oxides, black ironoxides and brown iron oxides; carbon black, iron hydroxide, graphite,black micaceous iron oxide; aluminum flake pigments, pearlescentpigments; calcium carbonate; calcium phosphate; calcium oxide; calciumhydroxide; bismuth oxide; bismuth hydroxide; bismuth carbonate; coppercarbonate; copper hydroxide; basic copper carbonate; silicon oxide; zinccarbonate; barium carbonate; barium hydroxide; strontium carbonate; zincoxide; zinc phosphate; zinc chromate; barium chromate; chrome oxide;titanium dioxide; zinc sulfide and antimony oxide.

Non-limiting examples of organic pigments include Monoazo (arylide)pigments such as PY3, PY65, PY73, PY74, PY97 and PY98; Disazo(diarylide); Disazo condensation; Benzimidazolone; Beta Naphthol;Naphthol; metal-organic complexes; Isoindoline and Isoindolinone;Quinacridone; perylene; perinone; anthraquinone; diketo-pyrrolo pyrrole;dioxazine; triacrylcarbonium; the phthalocyanine pigments, such ascobalt phthalocyanine, copper phthalocyanine, copper semichloro- ormonochlorophthalocyanine, copper phthalocyanine, metal-freephthalocyanine, copper polychlorophthalocyanine, etc.; organic azocompounds; organic nitro compounds; polycyclic compounds, such asphthalocyanine pigments, quinacridone pigments, perylene and perinonepigments; diketopyrrolo-pyrrole(DPP) pigments; thioindigo pigments;dioxazine pigments; quinophthalone pigments; triacrylcarbonium pigments,and Diaryl pyrrolopyroles, such as PR254.

Non-limiting examples of suitably insoluble organic pigments, groupedaccording to the color they produce (e.g. blues, blacks, greens, yellow,reds and browns), based on their color index include: Pigment Yellows11, 3, 12, 13, 14, 17, 81, 83, 65, 73, 74, 75, 97, 111, 120, 151, 154,175, 181, 194, 93, 94, 95, 128, 166, 129, 153, 109, 110, 173, 139, 185,138, 108, 24; Pigment Oranges 5, 36, 60, 62, 65, 68, 61, 38, 69, 31, 13,34, 43, 51, 71, 73; Pigment Reds 3, 4, 171, 175, 176, 185, 208, 2, 5,12, 23, 112, 146, 170, 48, 57, 60, 68, 144, 166, 214, 220, 221, 242,122, 192, 202, 207, 209, 123, 149, 178, 179, 190, 224, 177, 168, 216,226, 254, 255, 264, 270, 272; Pigment Violets 32, 19, 29, 23, 37;Pigment Browns 25, 23; Pigment Blacks 1, 31, 32, 20; Pigment Blues 15,15:1, 15:2, 15:3, 15:4, 15:6, 16, 60; and Pigment Greens 7, 36.

Non-limiting examples of suitably insoluble water repellents includeparaffin wax, olefin wax, petroleum wax, carnauba wax; polyethylene wax,silicone wax, polypropylene wax, PTFE wax and synthetic wax.

Non-limiting examples of suitably insoluble anti-weathering agentsinclude pigments such as zinc oxide, zinc sulfide, iron oxide, carbonblack, titanium dioxide; UV absorbers such as hydroxyl-substitutedbenzophenones, hydroxyphenyl benzotriazides, substituted acrylonitriles;UV stabilizers such as hindered amine light stabilizers (HALS); andanti-oxidants such as amines, imidiazoles or complex hindered phenolics.

Non-limiting examples of suitably insoluble dimensional stabilizationagents include waxes such as paraffin wax, olefin wax, petroleum wax,carnauba wax, polyethylene wax, silicone wax, polypropylene wax, PTFEwax and synthetic wax, and polymers such as polystyrene, polyethylene,polypropylene, polyvinyl chloride, polyacrylonitrile, polyvinyl acetate,polyester, acrylic polymers, polyamide, polyurethane, phenolic novolacs,phenolic resoles, urea formaldehyde resins, melamine formaldehyderesins, epoxy resins, natural resins such as rosin and rosin esters,hydrocarbon resins, ketone resins, terpene resins, alkyd resins,silicone resins and silicate resins, and other water insoluble polymers.

Non-limiting examples of suitably insoluble fire retardants are: metalhydroxides such as aluminum trihydroxide and magnesium hydroxide;antimony compounds such as antimony trioxide, antimony pentoxide andcalcium antimonite; zinc compounds such as zinc stannate, zinchydroxyl-stannate, zinc borate, zinc silicate, zinc phosphate, zincoxide and zinc hydroxide; phosphorous based compounds such as phosphateesters red phosphorus melamine phosphate, zinc phosphate, calciumphosphate, magnesium phosphate and ethylenediamine phosphate; silicatecompounds such as calcium silicate, silica, magnesium silicate and zincsilicate; halogenated compounds such as tetra bromo. bisphenol A;nitrogen based compounds such as melamine and its salts, melamine borateand polyamides.

Inorganic metal compounds, many having a degree of biocidal activity,can be used as additives in the compositions of the present invention.Non-limiting examples of such additives are suitably insoluble compoundsof, for example, copper, tin, silver, nickel. For example, non-limitingexamples of specific suitably insoluble metal compounds include cuprousoxide, cupric oxide, copper hydroxide, copper carbonate, basic coppercarbonate, copper oxychloride, copper 8-hydroxyquinolate, copperdimethyldithiocarbamate, copper omadine, and copper borate.

The micronized additive can be obtained by grinding the additive,optionally wetted or present as a dispersion, to the desired particlesize using a grinding mill Other particulating methods known in the artcan also be used, such as high speed, high shear mixing or agitation.The resulting particulate additive can be mixed with water or otheraqueous liquid carrier to form a solution of dispersed additiveparticles. Optionally, the: solution can comprise a thickener, such as,for example, a cellulose derivative, as is known in the art. Thesolution can, optionally, additionally comprise other biocides, organicor inorganic, micronized if desired, to produce a formulation suitablefor the preservation of wood and other cellulose-based materials.

The particles are preferably dispersed in a dispersant, such as acryliccopolymers, aqueous solution of copolymers with pigment affinity groups,modified polyacrylate, acrylic polymer emulsions, modified lignin andthe like. If desired, a stabilizer as is known in the art can be used.

The penetration of the dispersion formulation into the cellularstructure of wood or othercellulose-based material is dependent uponparticle size considerations. If the inorganic/organic additive sourceused in formulating the dispersion formulation disclosed herein has aparticle size in excess of 30 microns, the particles may be filtered bythe surface of the wood and thus may not be uniformly distributed withinthe cell and cell wall. As shown in FIG. 1, the primary entry andmovement of fluids through wood tissue occurs primarily through thetracheids and border pits. Tracheids have a diameter of about thirtymicrons. Fluids are transferred between wood cells by means of borderpits.

Without desiring to be bound by theory, penetration of the micronizeddispersion formulation into wood takes place because particles migrateinto or are taken up by tracheids in the wood. FIG. 1 shows thephysiological structure of wood. As shown in FIG. 1, the primary entryand movement of fluids through wood tissue occurs primarily through thetracheids and border pits. Fluids are transferred between wood cells bymeans of border pits. Wood tracheids generally have diameters of around30 microns, and thus good penetration can be achieved by the use ofparticles having long axis dimensions (“particle size” which are lessthan the tracheid diameters of the wood or wood product to be treated.Particles having diameters which are larger than the average diameter ofthe tracheids will generally not penetrate the wood (i.e., they will be“filtered” by the wood) and may block, or “clog” tracheids from takingin additional particles.

The diameter of the tracheids depends upon many factors, including theidentity of the wood. As a general rule, if the additives disclosedherein have a particle size in excess of 25 microns, the particles maybe filtered by the surface of the wood and thus may not be uniformlydistributed within the cell and cell wall.

Studies by Mercury-Porosimetry technique indicated that the overalldiameter of the border pit chambers typically varies from a severalmicrons up to thirty microns while, the diameter of the pit openings(via the microfibrils) typically varies from several hundredths of amicron to several microns. FIG. 2 depicts the border pit structure forconiferous woods. Thus, in order to increase penetration and improve theuniformity of distribution of the particulate additive, the particlesize should be such that it can travel. through the pit openings.

In one embodiment particle size of the micronized particles used in thedispersion formulation disclosed herein can be micronized, i.e., with along axis dimension between 0.001-25 microns. In another embodiment, theparticle size is between 0.001-10 microns. In another embodiment, theparticle size is between 0.01 to 10 microns. If superior uniformity ofpenetration is desired, particle size of the additive used in thedispersion formulation disclosed herein should be between 0.01-1microns.

In addition to a recommended upper limit of 25 microns, Particles whichare too small can leach out of the wood over time. It is thus generallyrecommended that the particulate additive comprise particles which havediameters which are not less than 0.001 microns.

Particles which are too large can clog the wood, preventing it fromtaking in other particles and particles which are too small can leachfrom the wood. Thus particle size distributional parameters can affectthe uniformity of particle distribution in the wood, as well as theleaching properties of treated wood. It is thus preferable to useparticle size distributions which contain relatively few particle sizesoutside the range of 0.001 to 25 microns. It is preferred that no morethan 20 weight percent of the particles have diameters which are greaterthan 25 microns. Because smaller particles have an increased chance ofleaching from the wood, it is also preferred that no more than 20 wt %of the particles have diameters under 0.001 microns. Regardless of theforegoing recommendations, it is generally preferred that greater than80 wt % of the particles have a diameter in the range of 0.001 to 25microns. In more preferred embodiments, greater than 85, 90, 95 or 99 wtpercent particles are in the range of 0.001 to 25 microns. For increaseddegree of penetration and uniformity of distribution, at least 50 wt %of the particles should have diameters which are less than 10 microns.More preferred are particle distributions which have at least 65 wt % ofthe particles with sizes of less than 10 microns. In an additionalembodiment, less than 20 wt % of the particles have diameters of lessthan 1 micron.

The present invention also provides a method for preservation of wood.In one embodiment, the method comprises the steps of treating wood witha composition (treating fluid) comprising a dispersion of additiveparticles. In another embodiment, wood is treated with a compositioncomprising a dispersion comprised of particles of multiple additives, atleast two of said additives having different average particle sizes. Thesize of the micronized particles of the additives is between 0.001 to 25microns, preferably between 0.001 to 10 microns, more preferably between0.01 to 10 microns and most preferably between 0.01 to 1 microns. Inanother embodiment, the wood is treated with a composition comprisingsoluble compounds and micronized additives.

The treating fluid may be applied to wood by dipping, soaking, spraying,brushing, or any other means well known in the art. In a preferredembodiment, vacuum and/or pressure techniques are used to impregnate thewood in accord with this invention including the standard processes,such as the “Empty Cell” process, the “Modified Full Cell” process andthe “Full Cell” process, and any other vacuum and/or pressure processeswhich are well known to those skilled in the art.

The standard processes are defined as described in AWPA Standard C1-03“All Timber Products—Preservative Treatment by Pressure Processes”. Inthe “Empty Cell” process, prior to the introduction of preservative,materials are subjected to atmospheric air pressure (Lowry) or to higherair pressures (Rueping) of the necessary intensity and duration. In the“Modified Full Cell”, prior to introduction of preservative, materialsare subjected to a vacuum of less than 77 kPa (22 inch Hg) (sea levelequivalent). A final vacuum of not less than 77 kPa (22 inch Hg) (sealevel equivalent) should be used. In the “Full Cell Process”, prior tointroduction of preservative or during any period of condition prior totreatment, materials are subjected to a vacuum of not less than 77 kPa(22 inch Hg). A final vacuum of not less than 77 kPa (22 inch Hg) isused.

The following examples are provided to further describe certainembodiment of the disclosure but are in no way limiting to the scope ofdisclosure.

EXAMPLE 1

Six hundred grams of red iron oxide, 400 g yellow iron oxide and 10 gcarbon black are added to a container containing 2850.0 g of water and150 g of a commercially available dispersant. The mixture ismechanically stirred for about 20 minutes and then added to a grindingmill. The sample is ground for about 1 hour and a stable dispersion isobtained. The particle size of the dispersed product can be analyzed byHoriba LA-910 Particle Size Distribution Analyzer (PSDA). The averageparticle size is preferably 0.3 microns with a distribution range of0.04 um to 1.5 um.

The resulting brown iron oxide dispersion can be diluted with water tomake a treating fluid containing 1.0% iron oxide. The treating fluid canbe used to treat southern pine samples using a full cell process. Thetreated samples can be oven dried and tested to check uniformdistribution of iron oxide throughout the cross sections and for thepresence of a uniform brown color.

EXAMPLE 2

Nine hundred grams of red iron oxide and 100 g yellow iron oxide areadded to a container containing 1550 g of water and 150 g of acommercially available dispersant. The mixture is mechanically stirredfor about 20 minutes and then added to a grinding mill. The sample isground for about 1 hour and a stable dispersion is obtained. Theparticle size of the dispersed product can be analyzed by Horiba LA-910Particle Size Distribution Analyzer (PSDA). The average particle size ispreferably 0.3 microns with a distribution range of 0.005 um to 1.5 um.

The resulting dispersion can be diluted with water to make a treatingfluid containing 0.5% total iron oxides. The treating fluid can be usedto treat southern pine samples using a full cell process. The treatedsamples can be oven dried and tested to check uniform distribution ofiron oxide throughout the cross sections and for the presence of auniform color.

EXAMPLE 3

Seven hundred grams of red iron oxide, 200 g yellow iron oxide and 5 gblack iron oxide are added to a container containing 2050 g of water and180 g of a commercially available dispersant. The mixture ismechanically stirred for about 20 minutes and then added to a grindingmill. The sample is ground for about 1 hour and a stable dispersion isobtained. The particle size of the dispersed product can be analyzed byHoriba LA-910 Particle Size Distribution Analyzer (PSDA). The averageparticle size is preferably 0.35 microns with a distribution range of0.005 um to 2.0 um.

The resulting dispersion can be diluted with water to make a treatingfluid containing 0.5% total iron oxides. The treating fluid can be usedto treat southern pine samples using a full cell process. The treatedsamples can be oven dried and tested to check uniform distribution ofiron oxide throughout the cross sections and for the presence of auniform color.

EXAMPLE 4

Eight hundred grams of yellow iron oxide, 100 g red iron oxide and 15 gorganic pigment blue PB 15 are added to a container containing 3000 g ofwater and 200 g of a commercially available dispersant. The mixture ismechanically stirred for about 20 minutes and then added to a grindingmill. The sample is ground for about 1 hour and a stable dispersion isobtained. The particle size of the dispersed product can be analyzed byHoriba LA-910 Particle Size Distribution Analyzer (PSDA). The averageparticle size is preferably 0.30 microns with a distribution range of0.005 um to 2.0 um.

The resulting dispersion can be diluted with water to make a treatingfluid containing 0.5% total iron oxides. The treating fluid can be usedto treat southern pine samples using a full cell process. The treatedsamples can be oven dried and tested to check uniform distribution ofiron oxide throughout the cross sections and for the presence of auniform color.

EXAMPLE 5

Five hundred grams of organic pigment yellow PY65, 600 g of organicpigments red PR23 and 15 g organic pigment blue PB 15 are added to acontainer containing 3000 g of water and 450 g of a commerciallyavailable dispersant. The mixture is mechanically stirred for about 20minutes and then added to a grinding mill. The sample is ground forabout 1 hour and a stable dispersion is obtained. The particle size ofthe dispersed product can be analyzed by Horiba LA-910 Particle SizeDistribution Analyzer (PSDA). The average particle size is preferably0.20 microns with a distribution range of 0.001 um to 2.0 um.

The resulting dispersion can be diluted with water to make a treatingfluid containing 0.25% total iron oxides. The treating fluid can be usedto treat southern pine samples using a full cell process. The treatedsamples can be oven dried and tested to check uniform distribution ofiron oxide throughout the cross sections and for the presence of auniform color.

EXAMPLE 6

Eight hundred grams of organic pigment yellow PY 13 and 100 g of organicpigments red PR254 are added to a container containing 4000 g of waterand 500 g of a commercially available dispersant. The mixture ismechanically stirred for about 20 minutes and then added to a grindingmill. The sample is ground for about 1 hour and a stable dispersion isobtained. The particle size of the dispersed product can be analyzed byHoriba LA-910 Particle Size Distribution Analyzer (PSDA). The averageparticle size is preferably 0.23 microns with a distribution range of0.001 um to 2.0 um.

The resulting dispersion can be diluted with water to make a treatingfluid containing 0.25% total iron oxides. The treating fluid can be usedto treat southern pine samples using a full cell process. The treatedsamples can be oven dried and tested to check uniform distribution ofiron oxide throughout the cross sections and for the presence of auniform color.

EXAMPLE 7

Five hundred grams of titanium dioxide is mixed with 450 grams of waterand 50 grams of commercially available wetting agents/dispersants. Themixture is mechanically stirred for 5 minutes. The mixture is thenplaced in a grinding mill and ground for about 30 minutes. A stabledispersion is preferably obtained with an average particle size of 0.29microns.

Forty grams of the above obtained titanium dioxide dispersion is mixedwith 960 g of water and the resulting composition can be used to treatsouthern pine stakes. The stakes can be tested for effectiveness againstUV degradation and discoloration and compared to untreated samples.

EXAMPLE 8

Three hundred grams of paraffin wax is mixed with 1855 grams of waterand 150 grams of dispersants. The mixture is mechanically mixed forabout 5 minutes and placed in a grinding mill. The mixture is ground forabout 90 minutes and a stable dispersion obtained with an averageparticle size of 0.282 microns. After grinding, 2000 g of water is addedto the dispersion and the final formulation is used to treat wood. Thetreated samples can be subjected to water repellency test following theprocedure described in American Wood Preservers' Association StandardE-4 “Standard Method of Testing Water Repellency of Pressure TreatedWood”.

EXAMPLE 9

One thousand grams of a commercially available acrylic polymer is mixedwith 3780 grams of water and 400 grams of wetting agents/dispersants.The mixture is mechanically stirred for about 20 minutes. The mixture isthen placed in a grinding mill and ground for about 120 minutes. Astable dispersion is preferably obtained with an average particle sizeof 0.20 microns.

A treating fluid can be prepared by mixing the above acrylic polymerdispersion with water and used to treat southern pine stakes. Thetreated stakes can be tested for water repellency.

EXAMPLE 10

One thousand grams of zinc borate is mixed with 3000 g of water and 200grams of commercially available wetting agents/dispersants. The mixtureis mechanically stirred for 20 minutes. The mixture is then placed in agrinding mill and ground for about 40 minutes. A stable dispersion ispreferably obtained with an average particle size of 0.399 microns.

A 3.0% zinc borate treating fluid can be prepared by diluting the aboveprepared zinc borate dispersion with water. Wood samples can be treatedwith the 3.0% zinc borate fluid and the treated samples can be ovendried. The samples can be tested for uniform distribution of zinc boratethroughout the cross sections. Thermal Gravimetric Analysis (TGA) andDifferential Thermal Analysis (DTA) tests can be carried out todemonstrate superior fire retardancy to untreated wood samples.

1-8. (canceled)
 9. A process for preserving wood, said processcomprising: a) providing a wood preservative composition comprising oneor more particulate additives comprising particles having diameters inthe range of 0.001 to 25 microns; b) applying said composition to woodsuch that at least some of the particles penetrate the surface of thewood.
 10. A process as in claim 9, wherein the additive is selected fromthe group consisting of inorganic pigments, organic pigments, waterrepellants, anti-weathering agents, dimensional stabilization agents,fire retardants and mixtures thereof.
 11. A process as in claim 9wherein fewer than 20 weight percent of the particles have a diameter ofgreater than 25 microns.
 12. A process as in claim 9 wherein fewer than20 weight percent of the particles have a diameter of less than 0.005micron.
 13. A process as in claim 9 wherein at least 50 weight percentof the particles have diameters in the range of 0.01 to 1 micron.
 14. Aprocess as in claim 9 wherein greater than 80 weight percent of theparticles have diameters which are less than 1 micron.
 15. A process asin claim 9, wherein greater than 85, 90, 95 or 99 weight percent of theadditive particles have diameters in the range of 0.001 to 25 microns.16. A process as in claim 9, wherein the additive is selected from thegroup consisting of iron oxides, carbon black, titanium dioxide paraffinwax, acrylic polymer, and zinc borate.
 17. A process as in claim 9,further comprising performing a) by grinding said additive intomicronized form.
 18. Wood comprising a wood preservative compositionwhich comprises a particulate additive which is inside the wood, whereinat least some of the particles of said additive have diameters in therange of from 0.001 to 25 microns.
 19. Wood as in claim 18, wherein theadditive is selected from the group consisting of inorganic pigments,organic pigments, water repellants, anti-weathering agents, dimensionalstabilization agents, and fire retardants.
 20. Wood as in claim 18wherein the additive is selected from the group consisting of ironoxides, carbon black, titanium dioxide paraffin wax, acrylic polymer,and zinc borate.